Thermal characterization of Li-ion cell electrodes by photothermal deflection spectroscopy

Inhomogeneous Temperature Distribution Affecting the Cyclic Aging of Li-Ion Cells. Part I: Experimental Investigation

“…The different cases are specified according to the applied external thermal boundary condition, although the internal temperatures deviated from this due to heat generation during operation. Considering the average ohmic resistance of around 14 mΩ at low frequencies (compare with Figure 4b) for the 9 A current, the intensive temperature control via the cells´ surfaces and tabs kept the internal temperature increase smaller than 1 K [21,25]. Figure 2a shows the reference cases with the three base temperatures, which were The temperature was measured using thermocouples type K connected to a NI 9213 thermocouple module (National Instruments Corporation, Austin, TX, USA) with a measurement sensitivity of up to 0.02 • C. For a precise measurement of the absolute temperature value, the thermocouples were calibrated with a linear correction between two reference temperatures against a PT25 resistance thermometer (Anton Paar GmbH, Graz, Austria) that again was calibrated according to ITS-90 (International Temperature Scale of 1990) with measurement uncertainties of <3.6 mK in the temperature range of −40 • C to 156 • C. The thermocouples were placed in the fluid supply and return lines, as well as pressed lengthwise onto the anode tab as close as possible to the electrode stack of one cell in each assembly.…”

“…The inhomogeneous temperature control was characterized by an imposed temperature gradient between these reference temperatures along the length of the cell. In these cases, the lower temperature was applied to the anode tab as its higher thermal conductivity [21] is advantageous for transient temperature control. In addition, the anode shows increased ageing at low temperatures [3,17].…”

“…The anode tab was chosen as the temperature measuring point for the cells since preliminary investigations based on the technique described by Schmidt et al [24] revealed that for the cells, the temperature at this point was closest to the internal cell temperature. This can be attributed to the fact that the in-plane thermal conductivity of the copper and aluminum current collectors is significantly higher than the thermal conductivity perpendicular to the electrode layers [21,25]. In order to additionally shield the thermocouple against environmental influences, the temperature of the tab was controlled on the side of the current flow and the thermocouple was attached to the opposite side where the voltage measurement was located and insulated with a thin plastic sheet.…”

“…This approach enabled a precise application of the targeted thermal boundary conditions with a very high temperature accuracy, which is not even feasible for the homogeneous steady conditions with the use of a climatic chamber. Figure 4b) for the 9 A current, the intensive temperature control via the cells´surfaces and tabs kept the internal temperature increase smaller than 1 K [21,25]. Figure 2a shows the reference cases with the three base temperatures, which were homogeneously applied.…”

Thermal conductivity and internal temperature profiles of Li-ion secondary batteries

“…In addition, the thermal conductivity of the graphite electrodes is reported to change for different graphite particle sizes, the relative amounts of polyvinylidene difluoride binder and carbon-black, and for different compaction pressures [27]. Last, the thermal conductivity is a function of temperature [27,28]. Using photothermal deflection In this paper we report the thermal conductivity for a wide range of pristine materials at different compaction pressures, dry, and soaked in electrolyte solvent.…”